This application claims the priority of German application number 196 45 340.2, the disclosure of which is expressly incorporated by reference herein.
Known hardenable phosphazene compounds have at least one ethylenically unsaturated side group, which can be radically or ionically polymerized. Examples of ethylene derivatives most frequently used as a polymerizable side group are acrylic, methacrylic, vinyl, allyl or styrol radicals.
European Patent Document EP-A-0 557 943 describes phosphazene compounds which can be hardened by radical polymerization and have at least one ethylenically unsaturated, polymerizable side group whose polymerization is initiated by the addition of initiators or by electron beams. European Patent Document EP-A-0 368 165 describes hardenable resin compositions which contain a hardenable phosphazene compound with at least one ethylenically unsaturated, polymerizable side group and, as additional essential constituents, a pentaerythritolacrylate compound and/or a bis-(4-acryloxydialkoxyphenyl) alkane compound. The polymerization of these resin compositions takes place by heating or ultraviolet radiation or electron beams.
As essential constituents of hardenable compositions, the known radically polymerizable phosphazene compounds have a number of disadvantages. For example, they tend to prematurely polymerize so that stabilizers have to be added to the compositions and high temperatures must be avoided. This, in turn, results in disadvantages with respect to the storage life and the selection of the synthesis conditions. During the synthesis, mild reaction conditions must be selected which reduce the yield since, frequently, under these reaction conditions, complete substitution of chlorine on the initial phosphazene cannot be achieved on the initial phosphazene by the side groups.
As a rule, the synthesized phosphazene derivatives are, therefore, not free of chlorine, which is also undesirable. The polymerization reaction of the known phosphazene derivatives, which as a rule takes place radically, is inhibited by atmospheric oxygen. Large initiator radicals must be used in order to achieve an acceptable hardening of the lacquer surface. In particular, the thermal hardening will frequently result in incompletely hardened surfaces. In the case of the hardening of radically polymerizing phosphazene resins, a considerable shrinkage will frequently occur, which results in an impairment of the adhesion and crack formation. For this reason, such phosphazene derivatives or mixtures thereof are unsuitable for many applications, for example, as lacquers, flat coats, or coating agents. To avoid shrinkage, large quantities of low-shrinkage additions are frequently used, which, however, may have other disadvantageous effects on the material characteristics of the hardened end product. European Patent Document EP-A-0 557 943, for example, describes the use of methacrylate derivatives or halogenated polyesters as shrinkage-reducing additions. Pure phosphazene resins, as described, for example, in European Patent Document EP-A-0 368 165, frequently have the disadvantage that their hardening takes place very slowly. If radically polymerizable phosphazene derivatives are used in lacquers or coating agents, the presence of radicals often results in discolorations, which frequently may not occur before the coatings age.
It is one object of the present invention to provide new hardenable compositions, which avoid the indicated disadvantages of the state of the art and furnish hardened products with improved characteristics. In particular, the invention provides a method to avoid a radical reaction mechanism during the harding of the compositions as well as compositions made from this method.
This object is achieved by means of hardenable compositions, which in the non-hardened condition, comprise as the essential constituent at least one phosphazene derivative of the general formula [NP--(X--Y--Z).sub.2 ].sub.n, wherein
each X is the same or different radical and is selected from the group --O--, --S--, NH-- or --NR-- (where R=C.sub.1 -C.sub.6 -alkyl); PA1 each Y is the same or different aliphatic, cycloaliphatic, aromatic and/or heteroaromatic hydrocarbon groups, which may optionally contain O, S and/or N; PA1 each Z is the same or different functional radical from the group --OH, --NH.sub.2, --NCO, --COOH, --CHO, --CH.dbd.CH.sub.2, allyl, N-methylol, acrylate, methacrylate, silyl, glycidyl or epoxy or preliminary stages of the radicals from this group or radicals from this group which are blocked by protective groups, in which case no more than four Z radicals may also be --H; and PA1 n is an integer of at least 3 and no more than 10;
and at least one cross-linking agent is provided, which has at least two functional groups selected among the Z radicals, which functional groups can react with the functional Z radicals of the phosphazene derivative.